feat: add ESLint with TypeScript support

Author: andrewshell

.husky/pre-commit

@@ -1 +1,2 @@
+pnpm lint
 pnpm test

eslint.config.js

@@ -0,0 +1,59 @@
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+  {
+    ignores: ['dist/**', 'node_modules/**', 'coverage/**'],
+  },
+  eslint.configs.recommended,
+  ...tseslint.configs.strictTypeChecked,
+  ...tseslint.configs.stylisticTypeChecked,
+  {
+    files: ['src/**/*.ts'],
+    languageOptions: {
+      parserOptions: {
+        projectService: true,
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+    rules: {
+      // Style rules matching existing code
+      'indent': ['error', 2],
+      'quotes': ['error', 'single', { avoidEscape: true }],
+      'semi': ['error', 'always'],
+
+      // TypeScript-specific adjustments
+      '@typescript-eslint/no-unused-vars': ['error', {
+        argsIgnorePattern: '^_',
+        varsIgnorePattern: '^_',
+      }],
+    },
+  },
+  {
+    // Test files are CommonJS - disable TypeScript checking
+    files: ['test/**/*.cjs'],
+    extends: [tseslint.configs.disableTypeChecked],
+    languageOptions: {
+      sourceType: 'commonjs',
+      globals: {
+        require: 'readonly',
+        module: 'readonly',
+        __dirname: 'readonly',
+        __filename: 'readonly',
+        process: 'readonly',
+        console: 'readonly',
+      },
+    },
+    rules: {
+      'indent': ['error', 2],
+      'quotes': ['error', 'single', { avoidEscape: true }],
+      'semi': ['error', 'always'],
+      'no-unused-vars': ['error', {
+        argsIgnorePattern: '^_',
+        varsIgnorePattern: '^_',
+      }],
+      // Disable TypeScript rules for JS files
+      '@typescript-eslint/no-require-imports': 'off',
+    },
+  }
+);

package.json

@@ -30,6 +30,8 @@
     "test": "pnpm build && c8 node --test test/*.test.cjs",
     "coverage": "c8 report --reporter=text-lcov",
     "typecheck": "tsc --noEmit",
+    "lint": "eslint src/ test/",
+    "lint:fix": "eslint src/ test/ --fix",
     "prepublishOnly": "pnpm build",
     "prepare": "husky"
   },
@@ -50,13 +52,16 @@
   "devDependencies": {
     "@commitlint/cli": "^20.2.0",
     "@commitlint/config-conventional": "^20.2.0",
+    "@eslint/js": "^9.39.1",
     "@types/node": "^25.0.0",
     "c8": "^10.1.3",
+    "eslint": "^9.39.1",
     "husky": "^9.1.7",
     "mockdate": "^3.0.5",
     "safe-buffer": "^5.2.1",
     "seedrandom": "^3.0.5",
     "tsdown": "^0.17.2",
-    "typescript": "^5.9.3"
+    "typescript": "^5.9.3",
+    "typescript-eslint": "^8.49.0"
   }
 }